The present invention relates generally to a seat belt restraint system and, more specifically, to a seat belt restraint system which changes configuration between a comfort configuration and a crash restraint configuration.
Automotive vehicle seats include a generally upright seat back mounted to a generally horizontal seat cushion for supporting a seated occupant. The seat back includes a top portion that often supports a headrest and a bottom portion that is often pivotally attached to the seat cushion for providing reclining adjustment of the seat back. The seat cushion extends between an inboard side (adjacent the center of the vehicle) and an outboard side (adjacent the door or side wall of the vehicle). A seat belt restraint system is commonly secured to the seat or the vehicle structure immediately adjacent the seat for restraining the seated occupant in the seat.
Currently, the most common type of seat belt restraint system is a three-point seat belt configuration. The three-point seat belt configuration is generally defined by a lap belt extending between the inboard and outboard side of the seat cushion and a shoulder belt extending diagonally from the outboard, top portion of the seat back to the inboard, bottom portion of the seat back. The lap belt and shoulder belt may be interconnected by a clasp or latch plate, and the clasp is releasably latched to a buckle on the inboard side of the seat cushion to fasten both the lap and shoulder belts around the occupant.
One type of seat belt restraint system utilizes a four-point seat belt configuration generally defined by a lap belt, usually made up of inboard and outboard lap belt segments extending from the respective inboard and outboard sides of the seat cushion toward the center of the seat cushion, and inboard and outboard shoulder belts extending downwardly from the top portion of the seat back adjacent the respective inboard and outboard side of the seat. When worn by an occupant of the seat, the four belt segments converge adjacent the center of the occupant""s pelvis and are secured to one another at a center latch point by a buckle and latch plate mechanism to complete the four-point seat belt configuration. Each of the four segments is preferably provided with a lockable retractor reel, allowing the segments to extend and permit freedom of movement, but which lock in response to an actual or anticipated crash of the vehicle. Belt pretensioners may also be provided for one or more of the segments, as is well known in the restraints art.
For any seat belt restraint system to achieve good protection of the seat occupant, it must be voluntarily worn. Therefore, occupant comfort of the system during normal, pre-crash use is an important consideration. It has been found that occupant comfort is enhanced if the lap belt segments extend substantially vertically downward after passing around the outsides of the occupant""s thighs, rather than extending rearward and downward at an angle. This more vertical orientation of the portions of the lap belt passing over the thighs also benefits restraint system performance by providing a downward pull on the shoulder belts, keeping them relatively taut and the center latch point positioned relatively low on the occupant""s pelvis. This low positioning of the center latch point is important to reduce the likelihood that during a frontal crash or other abrupt vehicle deceleration the occupant will slide underneath the lap belt, a phenomenon known as xe2x80x9csubmarining.xe2x80x9d
During a crash event, though, it is preferable that the lap belt segments extend somewhat rearward after passing around the outside of the occupant""s thighs. This rearward angle provides better restraint against forward movement of the occupant""s pelvis.
U.S. Pat. No. 4,221,403 discloses a mechanism whereby a seat belt anchor point slides rearward in response to a threshold level of vehicle deceleration. The mechanism, however, would be difficult to adapt to a system including belt pretensioners and/or belt retractors of the type that utilize a reel around which the belt is wound.
The present invention provides a vehicle occupant restraint system wherein a lap belt for a seat is movable between a comfort position wherein the portions of the belt extending over the outsides of the occupant""s thighs are generally vertical, and a crash restraint position wherein the same portions extend at an angle downward and to the rear. The lap belt is preferably augmented with shoulder belts to create a four-point restraint system.
The lap belt passes over the seat cushion and has opposite ends anchored adjacent opposite sides of a seat. The variable position of the lap belt is achieved by at least one belt guide disposed adjacent one side of the seat and positioned so that the lap belt engages the belt guide as it extends from the anchor point toward the seat cushion. During normal vehicle operations, the belt guide is located in a comfort position approximately below the desired position of the center latch point of the belt. The lap belt extends forwardly from the anchor point, engages the belt guide, then extends generally vertically upward toward the center latch point. Accordingly, the belt guides causes the portion of the lap belt passing over and around the outsides of the occupant""s thighs to have a relatively vertical orientation and thereby provide greater comfort. The vertical orientation of the lap belt between the center latch point and the belt guide also serves to provide a downward pull on the shoulder belt segments of a four-point belt system, keeping the shoulder segments relatively taut and the center latch point properly positioned relatively low on the occupant""s pelvis to inhibit xe2x80x9csubmarining.xe2x80x9d The lap belt is also easier for an occupant to don when in the comfort position, because the buckle/latch plate is farther forward, toward the knee, and so closer to the normal position of the hand when in a seated position. The occupant does not have to reach back toward the hip.
In the event of an actual or impending crash or other rapid vehicle deceleration, the belt guide moves rearward with respect to the comfort position, allowing the belt to extend in a substantially straight line to the rear-located anchor point. The lap belt thus extends downward and rearward at an angle to the vertical in order to provide better restraint against forward movement of the occupant""s pelvis.
The invention restraint system provides greater comfort during normal vehicle operation while still providing improved safety performance during a crash.
Other features and advantages of the present invention will be readily appreciated and better understood after reading the subsequent description when considered in connection with the accompanying drawings.